1. Field of the Invention
The present invention relates to a method for forming a scribed groove at the surface portion of a wafer so that the groove can act as the starting point for splitting the wafer to obtain chips by exploiting the cleaving property of the wafer and a scribing apparatus for implementing the method. The present invention particularly relates to a method for forming a scribed groove that can considerably reduce the amount of dimensional deviation between the scribed groove and the cleaved plane and a scribing apparatus for implementing the method.
2. Description of the Background Art
Semiconductor chips are produced by separating them from a wafer such as a laser diode wafer. In this case, scribed grooves are first formed at the surface portion of the wafer with a scribing apparatus. Then, a cleaving prism performs the cleaving work by concentrating the stress on the scribed groove. This is a well known technique. FIGS. 12(A) to 12(G) are schematic diagrams illustrating the process for producing chips from a wafer. First, electrode patterns 101 are formed on the surface of a wafer 100 (see FIG. 12(A)). Then, a scribing apparatus (not shown in the figure) forms scribed grooves 102 between the electrode patterns 101 from the edge of the wafer 100 (see FIG. 12(B)). A cleaving prism 103 having the shape of a triangular prism is pressed against the back face of the wafer 100 (the face where no electrode patterns are formed) along the scribed groove 102 (see FIG. 12(C)). The pressing operation cleaves the wafer 100 to obtain a number of bars, with the scribed groove 102 acting as the starting point of the cleavage (see FIG. 12(D)). Next, the scribing apparatus forms scribed grooves 102 between the electrode patterns 101 on the surface of the bar-shaped wafer 100a (see FIG. 12(E)). Finally, the cleaving prism 103 is pressed against the back face of the bar-shaped wafer 100a along the scribed groove 102 (see FIG. 12(F)). The pressing operation cleaves the bar-shaped wafer 100a to obtain a number of chips 100b, with the scribed groove 102 acting as the starting point of the cleavage (see FIG. 12(G)).
There are two commonly known methods for forming the foregoing scribed grooves: one method forms a linear groove by moving the cutting edge linearly, and the other method forms a boat-shaped groove by moving the cutting edge along an arc-shaped path. FIG. 13 is a diagram illustrating the method for forming a boat-shaped groove. The boat-shaped groove is formed by using a scribing apparatus provided with a cutting part 200 having a cutting edge 201. The cutting part 200 is moved such that the cutting edge 201 forms an arc-shaped path as shown by an arrow. In this case, cracks 114 are formed in a direction perpendicular to the groove.
However, the foregoing conventional groove-forming method has a drawback of a large amount of dimensional deviation between the scribed groove and the cleaved plane. FIG. 14 is a plan view showing a bar-shaped wafer which is cleaved after scribed grooves are formed by the conventional method. In obtaining chips from a wafer, it is desirable that the cleaving line be on the extended line of the scribed groove 102 as shown by a broken line 110, which is referred to as the intended cleaving line 110. With the conventional method, however, an actual cleaving line 111 does not coincide with the scribed groove 102 (the intended cleaving line 110) as shown in FIG. 14 in many instances. The amount of dimensional deviation 112 between the actual cleaving line 111 and the scribed groove 102 is no less than ±15 μm or so in the worst instance. As a result, the large deviation in the outside dimensions makes it difficult to produce chips with high yield ratio, and it is difficult to obtain chips having cleaved surfaces with high-quality mirror finish. When the amount of dimensional deviation in cleavage 112 is large, another problem is created. For example, when an LD chip 100b and an optical fiber 113 are placed as shown in FIGS. 15(A) and 15(13), if the end face 100c of the chip 100b is unproperly placed against the end face of the optical fiber 113 as shown in FIG. 15(B), the light-emerging position relative to the position of the chip deviates from the designed position, decreasing the efficiency of the optical coupling.